Earthmoving machines such as bulldozers, wheel loaders, and other earth moving equipment may alter a landscape of a worksite in accordance with a predetermined plan. The predetermined plan may specify certain dimensions and specifications of the worksite, and the earthmoving machines may alter the landscape accordingly. The predetermined plan may require work to be done by the earthmoving machines, such as covering the worksite with a particular material, excavating material from the worksite, or cutting the ground of the worksite to a finished predetermined profile. The machines may have an implement (e.g., a bulldozer blade) to carry out these actions.
Earthmoving machines may contain devices to aid operators in performing work on the worksite. One such device relates to positioning equipment configured to intermittently receive a horizontal position (or location) and a vertical position (or elevation) of the machine relative to the ground surface. Using the received information, the machine may have automatic controllers (e.g., an automatic implement control system) to adjust the implement to a desired height. For example, the automatic implement controller may move a blade on a bulldozer in an upward or downward direction based upon a difference between a detected elevation of the machine (e.g., a vertical position) and a target height of the blade (e.g., a desired vertical position depending on the predetermined plan). If the predetermined plan specifies, for example, that an elevation of the ground should be a certain level, the blade may be moved down to grade the ground to that level or up to cover the ground with material up to that level.
Currently, position information, such as the height (or the vertical position) of the blade, may be detected using several different techniques. One such technique involves receiving position information from a satellite positioning system, such as Global Position System (GPS), GLONASS or collectively to any Global Navigation Satellite System (GNSS). Satellite positioning systems include a constellation of satellites and require a satellite positioning receiver located on the earthmoving machine. The positioning receiver may receive position information from the satellite positioning system at a rate of 0.1 to 100 Hz and in practice may run at 10 Hz or 20 Hz.
Another positioning device is a robotic total station or automatic total station (ATS). The ATS includes an instrument which remotely determines the position of the implement, and sends signals to a receiver provided on the machine to adjust the implement position.
The instrument of the ATS uses a servomotor to track a machine and angle encoders to measure angles in a horizontal plane relative to the ground surface (x and y coordinates) and an elevation axis (z coordinate) relative to the ground surface. The instrument further includes an electronic distance meter, which transmits a laser beam of visible or infrared light to a prism or reflective surface provided on a machine. Light is then reflected back to the instrument which, in turn, calculates the distance between the machine and the instrument. Using the known position of the ATS, the measured angles and the measured distance, position information of the machine may be determined. Generally, an ATS locks onto the target as it moves around a worksite and constantly updates position information of the machine, which is used to adjust the implement if necessary. Current instruments may update at a rate of up to 6 Hz.
Another position device is a rotary laser, which rotates a laser beam to form an optical reference plane over the surface of the worksite at a rate of, for example, 600 RPM. The optical reference plane may be oriented vertically, horizontally, or at a known slope in one or two directions relative to the worksite surface. A photodetector device, which is typically mounted on the earth moving machine, receives light emitted by the laser, for example, at a rate of once every 100 msec, and generates a positioning signal in response thereto. A processor then controls the height of the implement based on the positioning signal.
Another position device is a fan laser, which rotates one or more fan shaped laser beams to enable a receiver to determine vertical angle or difference in elevations over the surface of the worksite at a rate of, for example, 3000 RPM. A photodetector device, which is typically mounted on the earthmoving machine, receives light emitted by the laser, for example, at a rate of once every 20 msec, and generates a positioning signal in response thereto. A processor then controls the height of the implement based on the positioning signal. An example of a fan laser is described in U.S. Application No. U.S. 2004/0125365 A1, which is discussed in further detail below.
Another type of positioning device is an inertial navigation system (INS), which determines position and attitude information of the earthmoving machine at a rate, for example, greater than 100 times per second. The INS may use an inertial measurement unit (IMU) that includes a set of sensors that measure six (6) degrees of freedom—three (3) linear degrees of freedom (such as x, y, and z coordinates in space) and three (3) rotational degrees of freedom such as (pitch, yaw, and roll). The linear degrees of freedom specify a position, and the rotational degrees of freedom specify attitude.
The IMU typically includes three (3) linear accelerometers for determining position and three (3) rate gyroscopes for determining attitude. Based upon the measurements of position and attitude, a computational unit, such as an analog circuit or microcontroller, may determine position and attitude information of the earthmoving machine. Mathematically, position information can be quickly determined by twice integrating a series of acceleration values obtained by the accelerometers, and the attitude information is determined by integrating once a series of rate measurements output from the rate gyroscopes.
Each accelerometer and rate gyroscope reading typically includes a relatively small amount of noise, which is summed during integration. The calculated position and attitude information is thus not precise, but can be known within a given degree of error. The INS, however, determines the position of the implement and updates the current position and attitude of the machine based on position and attitude information. Thus, although attitude and position information may be obtained within an acceptable margin of error, the error in such information, otherwise referred to as “drift”, can accumulate over time to an unacceptable amount. On a worksite, however, accurate machine position information is required over extended periods of time. Accordingly, INS systems typically have not independently been used to determine positions of earthmoving machines.
Typically, earthmoving machines may use one of GPS, ATS, fan laser, or plane laser positioning devices when carrying out earthmoving functions. For example, a GPS positioning device may be provided on the earth moving machine to determine location and elevation information of the machine. Although location information can be accurately obtained, elevation information is considerably more inaccurate. Accordingly, as disclosed in the above-noted U.S. Patent Publication No. U.S. 2004/0125365 A1 to Ohtomo et al., GPS and laser systems are combined to provide accurate elevation and location information.
In particular, Ohtomo et al. discloses a position measuring system that includes a fan laser and a photodetection sensor that receives a laser beam emitted from the rotary laser device. The photodetection sensor may be mounted on an earthmoving machine, and in response to light from the rotary laser device, may determine elevation information of the machine. Thus, in Ohtomo et al., the rotary laser system provides elevation information, which is more accurate than the GPS system. The earthmoving machine also includes a GPS receiver, which receives data for determining a location or horizontal position. In addition, location or horizontal information is obtained based on received GPS data.
The combined GPS and fan laser system disclosed in Ohtomo et al., however, generates position and elevation information less frequently than desired for automatic real time control of a cutting implement, for example, a blade. Accordingly, there is a need for a position monitoring system that can generate accurate position and elevation information with greater frequency and during periods when either or both of the GPS signals or the laser signals may be blocked.
The disclosed system is directed at overcoming one or more of the shortcomings in the existing technology.